1. Field of the Invention
The invention relates to an LED lighting device and to the uses thereof. LEDs (light-emitting diodes) are increasingly gaining in importance as light sources, for one, because they are considered to be energy efficient, and second, because they have a long lifetime and are thus expected to require low maintenance outlay.
2. Description of Related Art
An LED is an electronic semiconductor device. If power is supplied to it, it emits electromagnetic radiation, the wavelength of which can be in the infrared, visible and/or in the ultraviolet spectral range. The term LED, used in the present description, includes no limitation to a particular wavelength of the emitted radiation.
It is likewise possible for a plurality of emitting active elements to be mounted on a chip, which is likewise referred to as an LED in the context of the present description. Furthermore, no limitation in terms of the coherence length of the emitted radiation is associated with the term LED used herein either, such that laser diodes are likewise comprised by said term.
One property of LEDs which is disadvantageous for lighting applications, however, is based on the fact that commercially available LEDs are supplied in an encapsulation which includes a reflector and/or a lens which allow the radiation emitted by the LED to be irradiated forward at a relatively low viewing angle. Therefore, fluorescent tubes are still often used for lighting larger surface areas. Said fluorescent tubes, however, have the disadvantage that they can break easily, which is a problem in particular in applications in which strong vibrations or other mechanical stresses can occur, but also that they require a relatively high ignition voltage, which accordingly requires complicated electronic devices for the power supply and can likewise emit spurious electromagnetic radiation. Another disadvantage of fluorescent tubes is that they emit heat and UV radiation on their luminous surfaces.
In order to circumvent in particular the last-mentioned disadvantage, U.S. Pat. No. 4,733,332 proposes to couple light emitted by an incandescent lamp or gas-discharge lamp into the end face of a glass rod, which is provided with a line-shaped diffusion pattern on its lateral surface. The glass rod acts as an optical waveguide for the light that has been coupled in, the diffusion pattern couples it out of the glass rod in a manner in which it reflects the impinging light into the glass rod, allows it to pass through it and, on the opposite side of the glass rod, to be coupled out laterally therefrom. In this manner, a line-shaped lighting profile with a viewing angle, which can correspond to a fluorescent tube with reflector, is produced. Aside from the usual disadvantages of the proposed light sources, the proposed apparatus has the disadvantage that it cannot be used to produce light sources of arbitrary length in the form of luminous bands, because as the length of the glass rods increases, the brightness loss in the center of the glass rod would increase in an unacceptable manner.
EP 2063168 A1 describes an LED light system, in which the light emitted by the LEDs is coupled into the end face of an optical waveguide, which is mounted on a base section. The optical waveguide itself has, on its surface, no coating to direct the guided light perpendicular to the axis of the light system, but the base section includes the reflector, which is meant to ensure expanded emission angles. This lighting device has the disadvantage that the observer will perceive the optical waveguide quasi as a shadow in front of the reflector. Furthermore, the light must be coupled out of the optical waveguide and then be reflected by the reflector such that intensity losses must be expected. If such lighting devices are arranged one behind the other, an enormous brightness drop can be observed in the intermediate spaces, because the LEDs are mounted in their own packages on the base section and thus necessarily cause a large spacing between the optical waveguides which are arranged one behind the other. The disclosed LED light system cannot be used to realize a homogeneously emitting luminous band.